Design a subroutine called \"change_array\", which has the following function. T

Question

Design a subroutine called "change_array", which has the following function. The subroutine will process an array of longword-sized values stored in memory, as follows. For each value in the array, if it is more than 100, then change it to 100; if it is less than 0, then change it to a positive value with the same magnitude if it is not more than 100 and not less than 0, then change it to 0. The input parameters of the subroutine are: starting address and length (i.e., the number of longword-sized values) of the array to be processed. The two input parameters are passed by using address register A4 and data register D4, respectively. In other words, if your main program will call the subroutine to process a specific array, the main program should first store to A4 the starting address of the specific array, and store to D4 the length of the specific array, and then call the subroutine. In the subroutine, by using A4 and D4, it can locate the array to be processed. All registers used by the subroutine must be preserved. Also design one segment of your main program to call the subroutine to process a specific array which has 50 longword-sized values stored at memory starting from address 0x00002000.

Explanation / Answer

change_array(int*, int):

pushq %rbp

movq %rsp, %rbp

movq %rdi, -24(%rbp)

movl %esi, -28(%rbp)

movl $0, -4(%rbp)

movl $0, -4(%rbp)

.L6:

movl -4(%rbp), %eax

cmpl -28(%rbp), %eax

jge .L2

movl -4(%rbp), %eax

cltq

leaq 0(,%rax,4), %rdx

movq -24(%rbp), %rax

addq %rdx, %rax

movl (%rax), %eax

cmpl $100, %eax

jle .L3

movl -4(%rbp), %eax

cltq

leaq 0(,%rax,4), %rdx

movq -24(%rbp), %rax

addq %rdx, %rax

movl $100, (%rax)

jmp .L4

.L3:

movl -4(%rbp), %eax

cltq

leaq 0(,%rax,4), %rdx

movq -24(%rbp), %rax

addq %rdx, %rax

movl (%rax), %eax

testl %eax, %eax

jns .L5

movl -4(%rbp), %eax

cltq

leaq 0(,%rax,4), %rdx

movq -24(%rbp), %rax

addq %rdx, %rax

movl (%rax), %eax

movl -4(%rbp), %edx

movslq %edx, %rdx

leaq 0(,%rdx,4), %rcx

movq -24(%rbp), %rdx

addq %rdx, %rcx

cltd

xorl %edx, %eax

subl %edx, %eax

movl %eax, (%rcx)

jmp .L4

.L5:

movl -4(%rbp), %eax

cltq

leaq 0(,%rax,4), %rdx

movq -24(%rbp), %rax

addq %rdx, %rax

movl $0, (%rax)

.L4:

addl $1, -4(%rbp)

jmp .L6

.L2:

nop

popq %rbp

ret

main:

pushq %rbp

movq %rsp, %rbp

subq $48, %rsp

movl $1, -48(%rbp)

movl $-10, -44(%rbp)

movl $0, -40(%rbp)

movl $99, -36(%rbp)

movl $100, -32(%rbp)

movl $-55, -28(%rbp)

movl $105, -24(%rbp)

movl $109, -20(%rbp)

movl $49, -16(%rbp)

movl $150, -12(%rbp)

leaq -48(%rbp), %rax

movl $10, %esi

movq %rax, %rdi

call change_array(int*, int)

movl $0, %eax

leave

ret

# 1, -10, 0 , 99, 100, -55, 105, 109, 49, 150 array values and n = 10

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